[gn build] Port b68e2eb

Author: llvmgnsyncbot

llvm/utils/gn/secondary/libcxx/include/BUILD.gn

@@ -287,6 +287,7 @@ if (current_toolchain == default_toolchain) {
       "__algorithm/shift_right.h",
       "__algorithm/shuffle.h",
       "__algorithm/sift_down.h",
+      "__algorithm/simd_utils.h",
       "__algorithm/sort.h",
       "__algorithm/sort_heap.h",
       "__algorithm/stable_partition.h",